Heretofore, barrier valves of the check valve type designed for installation in a subsea gas pipeline have included a pivotal clapper member which requires a special opening in the valve body for accommodating the installation and removal of the clapper shaft. The valve body of such valves also include an access opening permitting access to the valve internals which is closed by a cover member bolted to the valve body. When it becomes necessary or desirable to retrieve or replace the valve internals, it has been necessary for a diver to go down and manually remove the bolts from the cover member, lift the cover member, and remove the clapper from its clapper shaft connections. The diver next pulled the clapper shaft through the special shaft opening in the valve body, then reached into the access opening to retrieve the loose clapper. The design of the prior valves, by virtue of the special valve body opening required for the clapper shaft, increases the possibility of leakage. In addition, the repair, retrieval and/or replacement of the valve internals requires a dangerous manual procedure which is also time consuming and costly.